This invention relates generally to flexible packages, and more particularly to flexible packages for holding fine particulate materials under vacuum while allowing any gas within the package to escape to the ambient atmosphere via a degassing valve in a wall of the package.
Various types of flexible packages for holding particulate materials, e.g., ground or whole bean coffee, chemicals, etc., under vacuum have been disclosed in the patent literature and are commercially available today. Examples of such packages are found in the following U.S. Pat. No. 4,576,285 (Goglio), U.S. Pat. No. 4,705,174 (Goglio), U.S. Pat. No. 4,913,561 (Beer), and U.S. Pat. No. 4,953,708 (Beer, et al.).
As is known by those skilled in the art, major advantages of flexible packaging as compared to relatively rigid packaging, e.g., cartons, are that until the flexible package is filled it takes up very little volume, and after it is emptied of its contents it readily collapses. This reduces the bag volume to approximately that of the unfilled package. The former characteristic is a significant advantage insofar as storage is concerned, while the latter characteristic provides is a significant advantage from the standpoint of disposability. Both of these advantageous characteristics are due to the fact that flexible packages are not self-sustaining, i.e., they are formed of sheet materials which cannot sustain the shape of the package if not filled.
One common type of flexible package for holding goods under vacuum until the package is opened is the so-called "gussetted" package or bag. Typically such a package is formed from a web of flexible stock material, e.g., polyethylene, polyester, polypropylene, metal foil, and combinations thereof in single or multiple plies, into a tubular body, having a face panel, a back panel, and a pair of gussetted sides. Each gussetted side is formed by a pair of gusset sections and a central fold edge interposed between a pair of outer fold edges. The lower end of the bag is commonly permanently sealed, e.g., heat sealed, along a line extending transversely across the width of the bag close to its bottom edge. The top of the bag is commonly sealed transversely across the entire width of the bag in a number of ways to maintain the contents under vacuum until the bag is opened. Such action is frequently accomplished via a readily openable mouth, which when opened provides access to the contents of the bag. For example, in one prior art package the top seal is made peelable by modifying the sealant layer with a peelable coating or incompatible additive. Thus, when the seal is peeled apart the unsealed portions form an open mouth through which the contents of the package may be removed. Another approach to providing an opening or mouth for a flexible package is that of the heretofore identified U.S. Pat. No. 4,705,174 (Goglio). That package includes a peel strip applied to the inner surface of the package below the top edges. The strip provides an airtight interfacial seal which can be readily peeled apart to provide access to the interior of the package.
For many applications of peelably openable flexible packaging it is desirable to be able to reclose the package after its mouth has been peeled opened in order to retain the remaining contents in the package so that they do not spill out, and/or that odors do not emanate from the package when the contents are odoriforous, and/or that the contents be somewhat isolated from the ambient atmosphere. Reclosure of such packages has been accomplished in several ways. One way is to fold over the top portion of the package contiguous with the peeled-open mouth to form a flap and to then apply a small strip of adhesive tape or a small preprinted adhesive label onto a portion of the flap and a portion of the contiguous package to hold the flap in place.
Other types of flexible package are also disclosed in the patent literature and are commercially available. One such type of flexible package is commonly constructed in the form of a "pouch" or "sack" having a front panel and a rear panel secured together along their marginal edges, without the use of side gussets. This type of package has the shape of a somewhat flattened pillow. These pillow or pouch type packages typically include a mouth portion which is arranged to be opened to provide access to the contents of the package. The mouth may be constructed so that the front and rear panels forming the package are peelably connected to each other to enable them to be grasped to be peeled apart to open the mouth of the package. Alternatively, the mouth of the package can be made severable, such that it can be cut or torn to provide access to the interior of the package.
In order to vent gases out of a hermetically sealed flexible package (whether of the gussetted or pouch type) containing a product, such as ground coffee, etc., it is a common practice to include a one-way "degassing" valve in a wall of the package to allow gas produced by the product or air entrapped in the package to vent to the ambient atmosphere while precluding the ingress of air into the package. Some of the degassing valves used also include a filter disk made out of paper or some other filter material to prevent the ingress of particles or debris into the valve, since such action could clog up the valve. Notwithstanding, the existence of degassing valves having internal filtering means, e.g., filter disks, it has been discovered that in hermetically sealed packages for very fine particulate materials, the one-way degassing valve sometime becomes partially or totally clogged with those particles. This occurrence may cause the valve to shut down, e.g., the outlet port of the valve become fully occluded or blocked, to prevent gas within the package from exiting to the ambient atmosphere, or may cause the flexible valve member (disk) to lift off of the valve seat, whereupon the ambient atmosphere may gain ingress into the package through the now open valve. In either case, the effectiveness of the valve is compromised, if not nullified.
The present invention successfully overcomes this disadvantage of the prior art hermetically sealed packages by including in the wall of the package a panel of filter material which may be considered as a "pre-filter" to the valve.
Prior to the present invention, it was known to produce flexible packages where the entire structure of the package, i.e., all of its walls, were made up of a filtering material, e.g., spun-bonded plastic, such as that sold under the registered trademark "TYVEK" by E.I. du Pont de Nemours & Co., Wilmington, Del., apparently to create a "breathable" package. It is also known to construct flexible packages of a plastic material including either a "header" strip of filtering material at the end of the package or an isolated or circular strip of filtering material, e.g., TYVEK.RTM. to function to create a "breathable" package. The disadvantages to these two known products are that they do not provide complete or absolute barrier properties and therefore cannot serve as effective hermetically sealed packages.